This application claims the priority of German Patent Application Serial No. 100 58 050.5, filed Nov. 23, 2000, the subject matter of which is incorporated herein by reference.
The present invention relates to a radial piston pump, and more particularly to a radial piston pump adapted to pump corrosive fluids, such as clarified water.
In conventionally designed radial piston pumps, piston shoes are connected to pistons through ball-shaped heads and pressed by comparatively strong helical compression springs against flat support surfaces disposed on the outer circumference of a support ring. The support ring is arranged on an eccentric cylindrical longitudinal section of the pump shaft and can rotate relative to the pump shaft. The support ring has at least three support surfaces which are offset relative to one another by 120xc2x0. Depending on the number of pistons, the support ring can also have a larger number of support surfaces, for example five or seven support surfaces.
The radially outwardly directed forces are hereby transferred from the support surfaces to the piston shoes and hence also to the pistons, while the helical compressions springs ensure that the piston shoes remain pressed against the support surfaces when the pistons are displaced radially inwardly.
Helical compression springs can operate reliably for displacing both the piston shoes and the pistons inwardly as long as the radial piston pump is used for pumping non-corrosive fluids. However, helical compression springs used in pumps that are subjected to less benign fluids, such as clarified water or aqueous solutions containing only a small fraction of lubricants, can be subject to corrosion. Such radial piston pumps are employed, for example, in descaling systems or water-based hydraulic systems. This reduces the service life of the radial piston pumps. The maintenance intervals are also relatively short, which diminishes their overall economic viability.
It would therefore be desirable and advantageous to provide an improved radial piston pump, in particular for clarified water or an aqueous solution with a small fraction of lubricants, wherein the pistons can reliably move towards the pump shaft without raising concerns about corrosion problems.
According to one aspect of the invention, a radial piston pump has a support ring that is disposed on an eccentric longitudinal section of a pump shaft and can rotate relative to the pump shaft. The support ring includes at least three mutually offset flat support faces which are uniformly distributed about the circumference of the support ring. The support faces contact piston shoes connected with pistons that extend radially from the pump shaft. The piston shoes have radial flanges that engage from behind support rails disposed on the support ring. In this way, the piston shoes remain in constant contact with the support faces disposed on the support ring. Also provided are spring-supported pressure rings which secure the piston shoes on the support ring against rotation thereto. The spring force has to be only large enough to press the piston shoes against the support faces in all operating positions. The spring force is only intended to compensate for unavoidable manufacturing tolerances.
Because the spring-supported pressure rings are now located in a region of the radial piston pump apart from the actual pumped medium, these components are likely not subject to corrosion.
The service life of the radial piston pump and the maintenance intervals are extended, while the pump also becomes more economical.
To facilitate assembly and disassembly of the piston shoes and the pistons as well as maintenance, the pistons extend through guide bushing with an outside diameter that is greater than the diameter of the radial flanges of the piston shoes and also greater than the outside diameter of the pressure rings. In this way, the piston and piston shoes including the pressure rings can be installed and removed through the bores for the guide bushings. In addition, the wall thickness of the guide bushings can be adapted to pistons with different diameters, so that the volumetric displacement of the radial piston pump can be readily changed. This arrangement also significantly simplifies the manufacture of different types of pumps.
Advantageously, the support rails have mutually parallel top and bottom surfaces and are arranged on the inside of two peripheral edge ribs disposed on the support ring. This arrangement significantly simplifies the manufacture of the peripheral edge ribs and of the support faces, since only simple straight milling operations are required. In all other aspects, the support ring represents a simple lathe-turned part.
According to another advantageous embodiment of the invention, each radial flange of the piston shoes is provided along its periphery with two mutually parallel opposing flat surfaces which are spaced apart from one another by a distance that is smaller than the distance between two opposing support rails. In this way, the piston shoes can be inserted during assembly while keeping the flat surfaces aligned parallel to the support rails until the piston shoes contact the support surfaces. Thereafter, the piston shoes only have to be rotated by 90xc2x0, so that the radial flanges engage the support rails from behind and thereby establish a tension-proof and pressure-proof coupling between the support ring and the piston shoes.
Conversely, for disassembly of the piston shoes, the piston shoes only have to be rotated by 90xc2x0 until the flat faces are parallel to the support rails. The piston shoes can then be removed from the support ring in the radial direction.
According to yet another advantageous embodiment of the invention, the pressure rings include circumferential shoulders with a diameter that is smaller than the width of the support ring, but greater than the distance between two opposing support rails. In this way, the circumferential shoulders contact the support rails in the coupling position, which is the position where the support ring, pressure rings and piston shoes are coupled.
According to another advantageous embodiment of the invention, the pressure rings are provided with axial connecting pieces that are oriented away from the pump shaft. The circumferential shoulders have opposing mutually parallel flat surfaces with a spacing therebetween that is equal to the distance between two opposing support rails when a joining clearance is taken into consideration. In the coupling position, the flat surfaces engage between the piston shoes and the support rails and thereby determine the position of the piston shoes.
Advantageously, rotation between the parts is prevented by providing in the end faces of the circumferential shoulders transverse grooves which cooperate with radially extending attachment pins that are secured in the piston shoes adjacent to the radial flanges.
According to yet another advantageous embodiment of the invention, the pressure rings are pressed against the support rails by pressure springs, in particular helical compression springs, disposed between the pressure rings and the guide bushings.
The radial piston pump can be assembled as follows:
First, the piston shoes, with the pistons already connected, are inserted through the bores in the pump housing that receive the guide bushings until the piston shoes contact the support surfaces, while at the same time the flat faces on the radial flanges are kept aligned parallel to the support rails. The piston shoes are then rotated by 90xc2x0, so that the radial flanges engage the support rails from behind. Thereafter, the pressure rings are inserted through the ring gaps between the pistons and the walls of the bores in such away that the flat faces on the circumferential shoulders on aligned parallel with the support rails, so that the flat faces engage between the piston shoes and the support rails. In addition, the transverse grooves engage with the attachment pins, thereby reliably preventing the piston shoes from rotating relative to the support ring. Subsequently, the pressure springs are installed and the guide bushings are inserted into the bores until they contact a stop disposed on the inside end of the bores. The pressure springs are centered on the axial connecting pieces of the pressure rings and on the connecting pieces of the guide bushings.
The radial piston pump is disassembled in the reverse order.